Refractory and heat insulated induction heating head



June 13, 1950 REFRACTORY YAND HEAT INSULATED INDUCTION HEATING HEAD M. P. ALBERTSON, JR

Filed July 8, 1946 e ICT. 'L

EIGL

INVENTOR BYZ A TTORNE Y Patented June 13,V 1950 REFRACTORY AND HEAT INSULATED INDUCTION HEATING HEAD Meredith P. Albertson, Jr., Detroit, Mich., assignor, by mesne. assignments, to The Ohio Crankshaft Companfy, Cleveland, Ohio, a corporation of Ohio Application July 8, 1946, SerialNo., 681,193

3 Claims. l

This invention relates to heating heads as em ployed primarily for internal tube heating by electrical induction.

In the copending application of Harold A. Strickland, Jr., Serial No. 572,461 (now Patent No. 2,457,845, dated January 4, 1949), there is described an induction heating apparatus applicable to the heating of the internal bores of Workpieces, such as rifles and; the like, wherein the diameter of the bore gives rise to considerable difiiculty in obtaining adequate heat in the bore surface. An induction heatingl head is used in this prior application comprising a heating coil formed" of a hollow conductor and possessing` a core of ferromagnetic material to increase the heating capacity of the unit. This coil is enclosed in an` external insulating layer and is adapted to be moved in juxtaposition to but out of contact with the internal surface of the workpiece. By this means heat is developed in the workpiece surface. A ydiiiiculty in this former construction resides in the fact that in some. uses due to radiation and conduction. from the, heated surfaces of the workpiece, both the. coil and a powdered iron or other ferromagnetic core material are subject to such high temperatures as to modify the coil. or core structure. disadvantageously. i

Primarily, therefore, one of the objects of the invention is. to provide an induction heating head of, such structure as to prevent overheatingfof the coil and core. Another object is to provide a head structure: which will tend to prevent arcing from the head` to the workpiece. An additional object. is to provide an induction heating head which tends f3.0. resist twisting when passedinheating relationship. to a workpiece, thisL efEect being due to: the magnetic interaction of the adjoining surfaces and n'eqtuently resulting iny breaking of the coil connections.

A more specific object of the invention is the provision of an induction heating head adapted to lie adjacent to but spaced from the inner surface of an enclosing workpiece, the head' compris-- ing a coil formed of an electrical conductor; a ferro-magnetic core withinthecoil; a casing enclosing the side at one end ofthe coil; a refractory. electrically nonconductive7 iiller embedding the; coilconductor and spacing the' coil from the casing and; a` refractory surface material on the outside of,V the casingv andthe exposed end, of the coils.

Still. another specific object off the invention is an induction, heating. head comprising a coil famed; from; an, electrical conductor; a ferro.-

magnetic core within the coil; an inllexibl'e casingv enclosing the side and one endy of the coil; a layer of electrical strip insulation lining the inside of the casing and a4 granular filler embedding the. coil conductor and spacing the coil from the casing and` insulation layers.

Other objects of the. invention pertain to the various details of construction as. will appear on consideration of the following disclosure of a form of the invention which may be preferred.

' In the accompanying drawings:

Figure I is a, longitudinal section through the induction heating head, the support means for the head, and' the associated workpiece; and

Figure 2 is. a section taken along linesV 2 2 of FigureA 1' illustrating the. construction of the coil and corel elements of the head.

In Figure 1` the workpiece which may be a rifle tube or other workpiece, is shown as Verti- 'cally positioned with attachment means (not shown), at the upper end thereof for transmission of rotational and axial movement in progressive heatv treatment, Adapted for positioning within a A workpiece is a heating coil. unit, generally indii cated by the numeral 5 composed'. of aV coil 6, a,

f tory ferro-magnetic properties,E although other types ot cores, such as laminated sheet steel and`lv the like,I may: be used.. Thev insulating casing. a mayl consist of. glass tape,I glass. string@ mica, on similar substance possessing high electrical, in-4 sulation and dielectric characteristics. It,- formed; in a plural-ity of layers around the side and; base; o -f the enclosing the. nller materia-1. 8; which may'Y be; any suitable ceramic or ce.` ment, for; example. water or sauereisen. nements... This cemei-itermfbedsthe-ooil-,turns and has asus-- stantial thickness as showninthe drawing relaf tive. @tithe diameter cirthe coil conducto-rs. This, ller material should high; temperaaures; and possess high electrical resistivity and 2f. 161W coeiiicient. for heat. empansion-- Taha protector @un lit is. also: of;A inside-tiem maeterial. which possesses high dielectric; and'L elece trical resistivity characteristics.. it; should.y be. refractory' in; nature withv ai low heat; coefficiente for expansion., and.r Should have. the capa-bility ci:

3 resistance to the modifying effects of oil and water employed in the quench system. Suitable ma.- terials for this cup consist in glass, quartz, asbestos cement, steatite, sillimanite, or soap stone. The surfacing material for the cup may be the saine asthe filler material 8.

The head unit -as above described is supported within the tubular space of the workpiece by means of the coil terminals I2 and I3, the terminal I2 extending upwardly from the coil at one side thereof in extension of the top turn I4 of the coil, whereas the terminal I3 connects with the lower turn I5 of the coil by means of a central coil section Ii passing upwardly through the coil and core to the terminal I3.

The guide ring 20 for the heating head is placed directly above the head unit 5 and consists of a. cylindrical metal block having two vertically extending apertures, aperture 2l being relatively largeyand slightly oi centerwhereas aperture 2,2 is relatively small corresponding with the dimensions of the coil terminal I2 and is positioned adjacent the ring' edge directly in line with the terminal i2. Through the central opening 2| the terminal I3 extends into connection with a connecting tube 2t which in turn makes connection through the conical coupling 2li to the inner lead-in conductor 25 of the electrical circuit. This conductor is in the form of a shell having a relatively large interior space for the supply of coolant and is adapted to extend axially through the bore of the workpiece to the bus bar connections at the top of the apparatus. An insulation tube 3U is iitted snugly within the guide ring aperture 2| to extend substantially above and below the ring. This tube encloses the coil termina1 I3 and insulates electrically this terminal as well as prevents leakage of coolant from chamber 28.

Surrounding the inner conductor Eil is a casing 26 oI` insulation material, preierably a refractory substance, which extends also over the coupling 24 and connecting tube Surrounding the insulation casing and displaced therefrom is a metal tube 2l forming a shell of lesser thickness than that of the shelly 25 and constituting the outer conductor of the electric circuit. Connection is made to the coil terminal I2 by fixed engagement of the end of the shell 2l with the guide'ring 20, as shown in Figure 1 of the drawings. As clearly appears from this figure, the outer conductor is adapted to t relatively closely within the workpiece bore, and since the thickf ness` of the shell is relatively small, there is a degree of flexibility in this conductor which permits adjustment oi the s-ame relative to the workpiece. This is oi considerable importance in bores of substantial length and facilitates the utilization of the head for heating of exceptionally small bores.

vThe space between the insulation casing 26 and the outer conductor 2l is such as to permit the passage of coolant down to the space 28 formed between the ring and the contracted end 29 of the insulation. Thence the coolant may pass into the coil through the lead-in terminal I2 and outwardly through the terminal I3 and connector 23 into the interior space of the inner conductor 25.

By the arrangement as above described it appears that the induction heating coil 6 is spaced from the surface of the workpiece bore by a layer of flller material, such as ceramic or cement, layers of insulating material such as glass tape or mica, a rigid protector cup, such as quartz, and

an external insulating layer around the cup so that any tendency for an electrical discharge or arc to form between the coil turns and the workpiece is removed. Thus pitting of the copper of the coil with resultant deterioration, as Well as inefficiency in the actual heating operation, is reduced or prevented. It is pointed out further that the flow-back of heat from the workpiece to the coil and the associated core is greatly reduced by the presence of the intervening ller compound and the miscellaneous layers of insulating material having low heat conductivity. Maintenance of the coil temperature at a substantially uniform value insures uniformity in the current flow and, in conjunction with the absence of arcing, maintains the timing constants at a uniform value, thus preventing any change in the over-all heating characteristics of the apparatus. Noteworthy also is the rigidity of the structure in that the filler encasing enclosures, in conjunction with the protecting cup I0, prevents twisting action on the coil as it moves into heating relation with the workpiece, so that breakage of the coil lead-in connections or terminals i2 or I3 is prevented.

Modifications of the structure in adaptation thereof for varied uses may be made and hence no limitation is implied by the specic showing other than may be required by the claims hereto appended.

What is claimed is:

1. An induction heating head adapted to lie adjacent but spaced from the inner surface of an enclosing workpiece comprising a coil formed of an electrical conductor, a ferro-magnetic core within said coil, a casing enclosing the side and one end of said coil, a refractory electrically nonconductive filler embedding the coil conductor and spacing the coil from the casing, and a refractory surfacing material on the outside of said casing and the exposed end of said coil.

2. An induction heating head comprising a coil formed from an electrical conductor, a ferromagnetic core within said coil, an inflexible casing enclosing the side and one end of said coil, a layer of electrical strip insulation lining the inner side of said casing, and a granular ller embedding the coil conductor and spacing the coil from the casing and insulation layers, said ller being refractory and possessing high electrical resistivity and a low coefficient of expansion for heat.

3. An induction heating head comprising an electric coil, a ferro-magnetic core within said coil, an inflexible casing enclosing said coil, a layer of glass tape on the inside of said casing, and a cementitious ller embedding said coil and spacing the glass tape layer from the coil.

MEREDITH P. ALBERTSON, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

1. AN INDUCTION HEATING HEAD ADAPTED TO LIE ADJACENT BUT SPACED FROM THE INNER SURFACE OF AN ENCLOSING WORKPIECE COMPRISING A COIL FORMED OF AN ELECTRICAL CONDUCTOR, A FERRO-MAGNETIC CORE WITHIN SAID COIL, A CASING ENCLOSING THE SIDE AND ONE END OF SAID COIL, A REFRACTORY ELECTRICALLY NONCONDUCTIVE FILLER EMBEDDING THE COIL CONDUCTOR AND SPACING THE COIL FROM THE CASING, AND A RE- 